Since World War II, metalated sulfurized alkylphenols have formed one of the backbones of lubricating oil detergent chemistry. Such chemicals have mostly one sulfur atom linking two and sometimes more alkylphenol units. In the absence of carbonation, the TBNs of these materials are generally 80-150BN.
As a class, metalated sulfurized alkylphenols have provided deposit inhibition and base for neutralizing the acids of combustion. Now, however, due to environmental concerns and legislative efforts, it is desirable to limit the amount of sulfur in lubricating oils and lubricating oil additive components, thus necessitating the development of sulfur free versions of these important detergents. In addition, there is a need to introduce some ashless base since high ash has proven to be problematic for certain catalyst systems.
It has now been discovered that use of alpha amino acids such as glycine and alanine together with alkylphenol, an alkaline earth metal base and a source of formaldehyde at high temperatures in the presence of certain polar catalysts and co-solvents afford oligomeric structures which are sulfur free with a corresponding metal-based TBN from about 100 to about 150BN, and furthermore which have significant ashless base due to the basic nitrogen of the alpha amino acid. The alpha amino acid is thought to be ionically attached to the phenolic oxygen via a calcium bridge as evidence by the fact that the alpha amino acid and its nitrogen is lost following acidification and water wash. This ionically attached nitrogen is in contradiction with the formation of a Mannich reaction as disclosed for example in U.S. Pat. Nos. 2,717,263 and 4,655,949.